Process of rectification



May 8, 1934 s. C..CARNEY PROCESS 0].:1` REGTIFICATION Filed July 29,1931 2 sheets-sheet 1 E; h mm. S n Q m .mmofm 2 en E wmofm o* Nn @m s NMn i w m 4 v 3 n? Z u www wwf fn #n o \r #n l m m R, m \1 m w Bw* m Il\\k duw I .m C :l "m C A \.!A fw MV Il .u UNM In D vn w w A u? w ,a ,Twm d En m s m www R R S R s R mg S Nm Q E Q Q E E mm a a s uJ e n nl m A.m H ul nD May 8, 1934. s. c. cARNEY PRocEss oF RECTIFICATION Filed July29, 1931 2 Sheets-Sheet 2 Patented May, 1934 UNITED STATES PATENT OFFICEraocnss or aEc'rmcATroN Application Jill! 29, 1931, SerialNo. 553,825

Claims.

This invention relates to the rectification of liquids and morespeciilcally to the rectillcation of mixtures of hydrocarbons though notneces- 'sarily confined thereto. l

This method of fractionation is applicable to the fractionationl o! anymixture which canA be fractionated, such as hydrocarbon mixtures,

mineral oils, products of destructive distillation of organic matter,fermentation products, such as; alcohols. organic acids, esters, etc.,mixtures or solutions of distillable (not azeotropic) chemicalsubstances either synthetic or otherwise produced or found in nature,etc.

The object of the invention is to provide a method of rectification,whereby a definite liquid chemical compound is produced substantiallypure. v

My invention. is particularly adapted to the 4rectification of lighthydrocarbon products containing oleilnes derived from cracking petroleumoils and produces a certain definite oleilne or certain denite olerlnesin a substantially pure condition. Heretofore by the conventionalmethods and system of rectification, it 'has beenimpossible to produce asubstantially pure product consisting of definite oleilnes.

' In the process of manufacturing alcohols from oleflnes, contained incracked petroleum products it is particularly desirable to use a puredefinite oleiine to obtain a pure alcohol. If the raw olene materialcontains variable proportions of the ,active olenes and other chemicallyactive ingredients, this process results in a chaotic complexity ofreaction products. As most commercial alcohol products consist of suchcomplex mixtures of alcohols, it reveals the fact that A. the methods ofrectillcation, used in the renery practice as hitherto known, areinsumcient for preparing materials suitable for the efilcient 40manufacture of alcohols, because they are not able to separate thedifferent olenes sharply enough. l

My new process of rectiilcation operates with' sufficient -accuracy toobtain a product which eliminates the major part of the diiliculties inmaking alcohols from oletlnes and permits simplication of that processand gives an excellent.

yield and a product of high purity.

Though applicable in general to' the 'rectiilcation of liquids, asillustration of the method of my invention, I shall describe its use inproduc-4 ing from commercially cracked petroleum products, a mixture ofA-butylene and isobutylene .vith a minimum of isobutane and normalbutane,

especially suitable for themanufacture of secondary butyl alcohol.

As is known in the and the manufacture of alcohols from olenes art ofpetroleum cracking,

contained in cracked products, there are available, either as vapors oras liquids, very'large quantities of hydrocarbons ranging from methaneto hexanes and hexylenes inclusive, the higher hydrocarbons usuallybeing separated by the present conventional rectifying methods. Thechief hydrocarbons, and their boiling points, conftained in such lighterconventionally rectiiled petroleum products are:

Boiling point Methane f -160 C. Ethane 86 C. Ethylene -103 C. Propane-45 C. Propylene -49 C. Isobutane -11 C Isobutylene -6 C. A butylene -5C. Normal butane V +1 C. Trans B butylene C. Cis B butylene +3 C.Pentane +36. 3 C. Amlenes +31-42 C.

My invention provides a process to produce for Y example from thisstarting material a material containing or more of A- and isobutylene,the remainder being either isobutane or normal butane or both. In actualpractice on commercial scale a product of 92% of 'A- and isobutylene hasbeen produced. vThe total sulfur content of this product produced in myprocess of rectiilcation is from .02% to .05% by weight as against .3%by weight or higher o f the feed.

Excluding negligible,` minor ingredients, the

principal components, and their boiling points of the starting materialare as follows:

Boiling point Isobutane -11 C. Gamma or isobutylene 6 C. A butylene -pv5' C. Normal butane -l- 1C. Trans B butylene .l\ C. Cis B butylene 3 C.

It will benoted that propane, the next lighter fraction, has a boilingJpoint 'of-45 C., while the amylenes, the next heavier fraction, start at31 C., so that it is comparatively easy to separate these substantiallyfrom the butane-butylene fraction, but the di'iculty overcome by myinvention rests in obtaining A and isobutylene or the B butylenesseparately from this fraction.

Before discussing further rectification of this fraction,- reference ishad to the accompanying drawings, from which my invention may be morereadily understood. 'Ihe drawings are diagrammatic views of apparatus bywhich the process of my invention may be performed. In the drawings,Fig. 1 represents a rectifying column receiving a feed inlet pipe 5, 5aand 5b, controlled by valve 6, 6a and 6b, and coming from a source notshown. The lower end of column 1 is provided with heating element 7 andthe bottom is provided with an outlet pipe 8 controlled by a levelcontrol Valve 9 and going to a storage tank not shown. The top of columnl is provided with a vapor line 10 going over into a reflux condenser 11having a cooling coil 12 and a bottom connection 13. Pipe 13 terminatesinto a T dividing into a reflux line 14 controlled by valve 15 andconnected with column 1. Branch 16 controlled by valve 17, 17a, 17h and17o connects to different points of rectifying column 2. This column hasat the lower, end a heating element 18 and is provided with bottomoutlet pipe 19 controlled by the valve 2U going over to the suction of apump 21 which discharges through a pipe 22 controlled by valve 23, 23a,23h and 23e into rectifying column 1. The top of rectifying column 2 isprovided with a vapor pipe 24 connecting to a reflux condenser 25 havinga cooling coil 26 and a bottom outlet pipe 27. Pipe 27 branches linto areux line 28 controlledv byv valve 29 and connecting to rectifyingcolumn 2. Branch 30 controlled by valve 31, 31a, 31h and 31e connectswith rectifying column 3. This column is provided with the heatingelement 32 at the lower end and has a bottom outlet pipe 33 controlledby valve 34 and going` over into the section of pipe 35 dischargingintoa line 36 controlled by valve 37, 37a, 37b, 37e and 37d and going overinto rectifying column 2. The top of reetifying column 3 is providedwith a vapor outlet pipe 38 connecting to a reflux condenser 39 providedwith a cooling coil 40 and having a bottom outlet pipe 41.` The bottomoutlet pipe 41 branches into a reiiux line 42 controlled by a valve 43and connecting to rectifying column 3. Branch 44 controlled by valve 45,45a, 45h, and 45e connects to rectifying column 4. This column isprovided with heating element 46 and a `bottom outlet pipe 47 controlled4by a liquid level control valve 48 and going to a storage not shown.'I'he top of column 4 is provided with a vapor line 49 connected to areflux condenser 50 having cooling coil 51 and a bottom outlet pipe 52.branches into a reflux line 53 controlled by a valve 54 and connected-to column 4. Branch 55 controlled by valve 5 6 goes to a storage tanknot shown. With apparatus as shown in the drawings, my processfor-father rectifying the fraction, ranging from isobutane to Cis Bbutylene inclusive, is performed as follows:

The feed, containing .the six butane-butylene components as mentionedbefore, is drawn from a source not shown and introduced thru pipe 5controlled by valve 6 in rectifying columnl at a point where the liquidon the plate corresponds I with 'the composition of the feed. 'I'hevapors from column 1 are condensed and the condensate -valve in thereflux or feed line.

Bottom outlet pipe 52 divided according to requirements into reflux forcolumn l and feed for column 2, as controlled manually by valves 15 and17 respectively. The quantity of reflux depends entirely upon theseparation to be made in the step under consideration. I prefer touse anautomatic column control based on the temperature gradient in the Kcolumn which maintains a constant difference in temperature between thetop of the column and a selected point considerably lower, bycontrolling the amountof reflux to column 1 or respectively the feed tocolumn 2; a change in difference of these two temperatures operates aThe top product of column 1 is taken as liquid 'and flows by pressuredifference as feed to a desired point of column 2. The bottom product ofcolumn l, drawn oif below the heating element 7, and comprising theheavier B butylenes and a part of the normal butane, not desired in thisexample, is pumped to storage. The bottom product of column 2, thefeed-back liquid for columzn 1, contains a higher concentration of thedesired A and isobutylenes than the original raw material but a lower;concentration than the top product of column 1 and for this reason isintroduced in accordance with its composition at a point in column llocated between the entrance of the original feed and the top plate atwhich point the liquid on the plate corresponds in composition to thefeed-back liquid. Provisions are made to enable the operator thru thema'- nipulation of various valves to introduce this feed-back liquid atthe correct point of column 1, thus intensifying the concentration ofthe A and isobutylenes in the top of column 1. The vapors leaving column2 are condensed and the condensate divided into reflux for column 2 andfeed` for column 3 in the same manner and for the same reason asdescribed heretofore at column 1. The flow of condensate is establishedpressure difference and isobutylenes in the column, resulting in aproduct of higher concentration. 'Ihe vapors leaving column 3 arecondensed and the cond ensate divided between column 3 and column 4 as'described before; The feed to column 4 flows by pressure difference andenters at a point usually high above the bottom of the tower, to obtaina sufficiently large safety factor in eliminating as top productsubstantially all isobutane ,with a. minimum amount of isobutylene, thusproducing a highly f concentrated fraction of the desired A andisobutylenes as bottom product of the column.

The vapors leaving column 4 are condensed and part of the condensate isused as reflux for column 4 While the balance goes to storage.

For illustration a table is given showing an example of operatingtemperatures andA pressures with the A and isobutylene content of thetop and bottom products of each column, all figures being approximateand only illustrative; The

feed used in this example-contains 40-45% butylenes, of which 20-25%comprises the desired lighter A and isobutylenes and 20% theV heavier Bbutylenes, which are eliminated.

c01- colmm mn isopresb l) un lone Per- ' Lbs. cent Top product 1 206 21056-60 ttom et l 217 0-5 Toppmuetz v 19o 11o ss-1o Bottopxsroduct? 10350-55 Top uct3 162 ll0 70-80 ttgllol'tnillmtq 156 60-65 Top uct4 1% 9520-30 Bottom product4 136 80-00 It is known that a commercial column,even a very eiiicient one with many plates, cannot concentrate theseolenes to a high percent however, in such a column it is quite wellpossible to produce a fraction containing a higher percentage' smallernumber of columns may be used, repre-- senting a larger or smallernumber of steps and depending upon the product desired.

I also prefer to use, for this extremely selective rectification,columns equipped with my method of establishingjinherent stability asdescribed in my copending patent application Serial No. 539,- '118;however, I do not wish to limit myself hereto, as mv process may beperformed in a plurality of any eillcient column of the conventionaltype.

Y feed containing a "paring From the foregoing illustration anddescription, it is clear that in my process, any desired fractionorsingle hydrocarbon can beobtained from araw material. l2 use theprincipleof pre the raw material in one column and producing there aproduct from'which it is possible to obtain in a subsequent column orcolumns the desired fraction by rectification. This method succeedsbecause it is easier. to obtain all of a component, Vif some `of thenext heavier or lighter be permitted to go with it as occurs in columnl, disregarding purity to obtain larger yield; and it isjeasier toobtain a product in purity from a high percentage of the desiredfraction if it is not required to obtain all of the desired fractionfrom the feed, disregarding yield to obtain highest purity. p

The progressively decreasing pressure from col'- umn 1 to column 4 maycase the feed back from one column to the preceding one-flows bypressure difference between the columns, while the feedfrom one columnto the next one has to be pumped. In fact the columns may be operatedunder any combination of progressively increasing or decreasingpressures.

In the 'illustrative example mentioned. an intermediate fractlon of thegiven'material was desired, but it will be understood that in case thetop fraction of a given material is desired, the desired produced wouldbe produced as top product of .column 4, while the bottom production ofcolbe reversed, in which umn4wooldbe-redbaekcolumamasimi1ar manner asheretofore described.

Figs. 2 and 3 of the drawings show two different arrangements of backfeed circuits in a fractionating Fig. 2 is an illustration of aprocessof multistage rectification in which column l receives the raw I ymaterial from storage, while column 2 produces a top product ofsubstantially the same composition as the raw material and therefore isfed back to column l at the same point as the feed from storage. 'Thefeed back of this product may be introduced at any point of column l, inaccordance with its composition.

Fig. 3 is an illustration of a process of multistage rectification, inwhich column 1 receives the feed from storage and column 2 produces,

from the bottom product of column l., a top product havingr the samecomposition as the raw material and therefore is fed back to column 1.atthe same point as the feed from storage. Columnv 3 receives the topproduct from column l as lfeed and produces a bottom product having thesame composition as the raw materialfwhioh therefore is fed back to thesame point as the feed to column l. It is imderstood that in thisfractionating system, the top product and bottom product back feed areintroduced'into this preceding column at a point where the liquid of thecolumn is accordance with the composition of the back feed v material.In this system, as in any othervherein described, the points ofreintroduction of either top or bottom back-feed are determined by its.composition. It is preferable to reintroduce the back-feed into a columnnear the plate which contains liquid having a composition correspondingto that of the back-feed. In the appended claims such points arereferred to as corresponding points. Y

In my process of multistaged rectification based on the back feedprinciple, I may employ the top pending upon the desired rectification.If selective rectification-of the ascending material of the first columnis desired, Iemploy the bottom baci: feed circuit as shown betweencolumns 1 and'3 of Fig. 3 and in' case selective rectificationv of thedescending materialof the first column is desired, I employ lthe topproduct back feed circuit. l In the former operation, the desiredproduct is produced. as top product from a column, and in the productorbottom product back feed circuit delatter as bottom product. With therst column g of a rectification system is meant the column, whichreceives the raw material from storage as feed. 4

In Fig. 1 of the drawings, the ascending material of column 1 is furtherrectified in columns 2 and 3 having the bottom back feed circuit whileproducingfthe rectified product as top product of column 3. The desiredproduct however, is anA intermediate fraction of the rawV material ofcolumn l and is the higher boiling fraction of the top product of columnA3. This top product is thus in turn rectified inv column.4 and, as inthe example, one tower is suicient to accomplish the separation of thelighter fraction from the heavier fraction, the desired product isproduced as bottom product from tower 4. In case the desiredfractionation can not be alone, additional columns have to'beadded.form-V obtained in column 4 v145 ingwith colnmn 4 a rectification systemin which l this column is operated as the first column of this systemand as further rectification of the descend- Y ing material of column 4is desired,` the additional columns have to operate with a top produc-tback feed circuit while the desired fraction is produced as bottomproduct of the last column.

I claim as my invention;

1. In a process of fractionating a fluid mixture in a series of stagesfor production of the desired product, the steps which comprisefractionating said mixture at one stage, thereby concentrating saidproduct in one portion of the mixture, diminishing its content in theother separate portion of the mixture, and forming and maintaining aseries of mixtures having intermediate compositions, separatelywithdrawing said two portions from this stage of the process, subjectingthe first portion of the mixture to a further fractionation in thesecond stage, whereby a secondary concentrate of the product and asecondary portion with the diminished content of the product and havinga composition intermediate of those of the first two portions of themixture are obtained, and returning atleast a part of the said secondaryportion to the corresponding point of the rst stage of. the process.

2. The process of fractionation wherein the secondary concentrateobtained in accordance with the claim l is further fractionated torecover a product of higher purity.

3. In a process of fractionating a uid mixture in a series of'stages forproduction of a relatively low boiling product the steps which comprisefractionating said mixture at one stage, thereby concentrating saidproduct in 'one relatively low boiling portion of the mixture,diminishing its content in the other separate relatively high boilingportion of the mixture, and forming and maintaining a series of mixtureshaving intermediate compositions, separately withdrawing sai-d twoportions from this stage of the process, subjecting the first portion ofthe mixture to a further fractionation in the second stage, whereby asecondary relatively low boiling concentrate of the product and asecondary relatively high boiling portion with the diminished content ofthe product and having a composition intermediateof those of the rst twoportions of the mixture' are obtained, and

returning at least a part of the-said secondary portion to thecorresponding pointof the first stage of the process.

4. In a process of fractionating a fluid mixture in a series of stagesfor production of a relatively high boiling product the steps whichcomprise fractionating said mixture at one stage, thereby concentratingsaid product in one relatively high boiling portion of the mixture,diminishing its content in the other separate relatively low boilingportion of the mixture, and forming and maintaining a series of mixtureshavingintermediate compositions, separately withdrawing said twoportions from this stage of the process, subjecting the rst portion ofthe mixture to further fractionation in the second stage, whereby asecondary relatively high boiling concentrate of the product and asecondary relatively low boiling portion with the diminished content ofthe product and having a` composition intermediate of those of the rsttwo portions of the mixture are obtained, and returning at least a partof the said secondary portion to the corresponding point of the firststage of the process.

5. In a process of fractionating a fluid mixture in a series of stagesfor production of one relatively low and the other relatively highboiling products, the steps which comprise fractionating said mixture atone stage, thereby concentrating the two products separately in twodifferent portions of the mixture and forming and maintaining a seriesof mixtures of intermediate compositions,

separately withdrawing said two portions from this stage of the processand subjecting them to further fractionation in separate stages; therebyproducing two corresponding relatively low and high boiling secondaryconcentrates of the products and two portions of the original mixturehaving intermediate compositions, and returning at least a part of atleast one of saidtwo portions to the corresponding points of the rststage of the process.

SAMUEL C. GARNEY.

